This invention relates to apparatus for milling a well casing, and more particularly to apparatus for milling a window at a desired position in one side of a well casing.
In the exploitation of oil and gas wells it is sometimes necessary to form an opening in the steel well casing. For certain applications the orientation of the opening relative to ground co-ordinates is important. It has been proposed to form such an opening by use of one or more milling tools and the present invention, in its preferred embodiment, provides apparatus for forming such an opening (hereinafter referred to as "a window") by means of a milling tool.